An increasing number of automobiles have air bag crash systems. The air bag is typically located on the steering wheel facing the driver. The air bag must be in continuous electrical connection with impact sensors in the car body. In the event of a crash, the impact sensor or sensors provide an electrical signal to the air bag crash assembly that instantly inflates the air bag. Accordingly, there is an essential need for a reliable electrical connection between the rotatable portion of the air bag assembly, which is mounted to the steering wheel, and the remaining portion of the assembly, which is mounted to the stationary steering column.
Electrical connections between rotatable and stationary parts are well-known. Typically, an electrical brush rests upon a conductive ring, with one of the parts being rotatable to provide a rotatable electrical connection. However, there is a risk, particularly during the impact of an accident, of transient failure of the electrical connection in the brush and ring system, which could result in failure of the entire air bag system crash assembly.
Accordingly, a clockspring has been previously developed. The clockspring typically includes a flat, flexible, ribbon cable wound around a rotatable hub. The rotatable hub is located on the steering column. The ribbon cable is contained within a housing. A first end of the ribbon cable is connected to a deployment unit of the air bag and a second end of the ribbon cable is connected to interconnectors which pass out of the housing. The interconnectors are connected to the impact sensor or sensors on a stationary location of the vehicle. In this manner, the deployment unit for the air bag is reliably connected to the impact sensors of the vehicle.
As discussed above, clocksprings were originally developed to provide a reliable connection between the steering wheel and the steering column for airbags. As clocksprings continue to develop, more and more accessory and instrument controls are being located upon the steering wheel and, as a result, are utilizing the clockspring for electrical connections to the steering column. These additional components are increasing the number of individual signal lines contained within the ribbon cable. Moreover, the electrical current requirements for individual signal lines are also increasing due to some of the high current devices being incorporated into the steering wheel.
Consumers continue to desire more and more comfort features with their automobiles. For example, one high current device or feature that may possibly be added to the steering wheel is a heating element. A conventional clockspring is not designed to handle such a high current device. Conventional practice would be to utilize a slip ring to transmit high electrical current between a steering wheel and a steering column. Unfortunately, slip rings have a tendency to generate unacceptable noise levels. Furthermore, slips rings wear over time causing degradation in performance.
Since clocksprings typically utilize thin ribbon cables with low amperage wiring, it can be potentially dangerous for high currents to flow through clocksprings. An uncontrolled high current in a clockspring could damage the vehicle and its instruments. Furthermore, resulting damage to the clockspring could likely defeat a major purpose of the clockspring: providing a reliable electrical connection for the airbag safety system. Moreover, such an uncontrolled current could cause a fire damaging the vehicle and seriously injuring a driver or passenger.
Accordingly, there is a need for a system of monitoring and controlling high current devices that utilize clocksprings.